1. Field of the Invention
The present invention relates to an illumination apparatus and projection display apparatus each utilizing fourth color component light in addition to red component light, green component light and blue component light.
2. Description of Related Art
Heretofore, there has been known a projection display apparatus including three light valves corresponding to three color light beams, a cross dichroic cube for combining light beams outputted from the three light valves, and a projector for projecting a light beam combined by the cross dichroic cube.
Here, the cross dichroic cube has three light incident surfaces which light enters and one light-outputting surface from which light is outputted. Accordingly, when light beams entering the cross dichroic cube are of three colors, a projection display device only needs one cross dichroic cube.
On the other hand, there has been also proposed a projection display device that utilizes light beams of four or more colors in order to improve color reproducibility and luminance. A projection display device utilizes, for example, orange, yellow or cyan in addition to three colors of red, green and blue, so that color reproducibility and luminance is improved refer to Japanese Patent Publication No. 2002-287247 (claims 1 and 4, FIG. 1, and the like), for example).
In a case where a projection display device uses light beams of four or more colors, the light beams of four or more colors cannot be combined by one cross dichroic cube. Accordingly, the projection display device is required to have a plurality of dichroic cubes (or cross dichroic cubes).
In a case where four color light beams need to be combined, for example, the projection display device obtains two combined light beams each composed of two color light beams, and further combines the two combined light beams to obtain a combined light beam of four color light beams. Incidentally, the projection display device may obtain a combined light beam of four color light beams by obtaining a combined light beam of three color light beams, and then by combining the obtained combined light beam with the remaining one color light beam. Instead, the projection display device may obtain a combined light beam of four color light beams by obtaining a combined light beam of two color light beams, and then by combining the combined light beam with the remaining two color light beams.
Here, the lengths of the optical paths from the light valves corresponding to the respective light beams of four or more colors to the projector need to be the same. In addition, a plurality of dichroic cubes (or of cross dichroic cubes) need to be provided between the light valves and the projector. This requires a projector to have a long back focus.
As a result, the projector used in the projection display apparatus that utilizes three color light beams cannot be used for another type of projection display apparatus that utilizes four or more color light beams. Accordingly, the entire costs for the projection display apparatus increase.